ECG criteria
- Look for a distinct low-amplitude deflection or "bump" immediately after the end of the QRS in leads V1–V3
- The wave is located between the end of the QRS and the beginning of the ST segment, prolonging the actual electrical activity of the ventricles
- The amplitude is usually small, on the order of tens of microvolts; there is no strict universal amplitude threshold, and increased calibration is often needed for reliable detection
- Correlate with other features of ARVC: T-wave inversion in V1–V3 in adults without complete right bundle branch block; terminal activation duration (TAD) ≥55 ms in V1–V3 measured from the nadir of the S wave to the end of the QRS, in the absence of complete RBBB
- Assess the QRS duration and the presence of partial right ventricular conduction delay, which may mimic or mask an epsilon wave
- When suspected, ensure a high-quality standard recording (if necessary, at 50 mm/s and 20 mm/mV, with minimized artifacts); use the signal-averaged ECG (SAECG) separately as a method to detect late potentials rather than to confirm the epsilon wave itself
What it looks like on ECG
An epsilon wave is a small additional deflection or notch that appears immediately after the end of the QRS complex and before the ST segment, predominantly in leads V1–V3 (technically reflecting delayed activation of the right ventricular free wall). Its amplitude is low, usually on the order of tens of microvolts; there is no strict universal amplitude threshold for its definition, and the wave is easily missed on standard recordings at a normal speed of 25 mm/s.
Electrocardiographically, this is a manifestation of delayed, fragmented depolarization of a myocardial region that is electrically "lagging" behind the main ventricular mass. In practice, the wave appears as a small upstroke or notch continuing the QRS into the zone where a smooth isoelectric line or ST segment should normally begin.
| Sign | Characteristic |
|---|---|
| Localization | V1–V3 |
| Position | between the end of the QRS and the ST segment |
| Amplitude | low, on the order of tens of microvolts, without a strict universal threshold |
| Associated findings | T-wave inversion in V1–V3, QRS widening in V1 |
An epsilon wave is often better visualized on extended recordings and with increased amplitude calibration. Late potentials can be sought separately from the wave itself using a signal-averaged ECG (SAECG) — this is an additional sign of the same substrate of delayed fragmented activation, but SAECG neither confirms nor replaces the visual identification of an epsilon wave on a standard ECG.
Mechanism
The underlying mechanism is usually fibrofatty replacement of the right ventricular myocardium, typical of arrhythmogenic cardiomyopathy (ACM, formerly arrhythmogenic right ventricular dysplasia). Areas of fibrosis and adipose tissue disrupt normal impulse propagation through the ventricular fibers, creating zones of delayed, heterogeneous depolarization.
These areas are activated with a delay relative to the bulk of the myocardium, and their electrical activity is recorded after the end of the normal QRS — presumably, this late fragmented activation of ventricular myocardial areas forms the epsilon wave on the surface ECG. Fibrofatty replacement in classical right ventricular ACM is one of the possible substrates; the modern concept of arrhythmogenic cardiomyopathy also includes left ventricular and biventricular phenotypes, so the finding itself is nonspecific and not a strict marker of a purely right ventricular process. These same zones of delayed conduction provide the substrate for the reentry mechanism of ventricular tachyarrhythmias typical of this disease.
Causes
- Arrhythmogenic cardiomyopathy (main cause, classically the right ventricular form)
- Cardiac sarcoidosis with ventricular involvement (can produce a similar picture)
- Chagas disease with right ventricular involvement (described in isolated cases)
- Pronounced surgical or post-infarction scar of the right ventricle (rare, similar mechanism)
Differential diagnosis
- Right bundle branch block: wide QRS with characteristic rSR' morphology in V1 and wide S in I, V6; complete RBBB and nonspecific terminal activation delay, as well as QRS fragmentation, can create epsilon-like notching, so differentiation on a single surface tracing is often difficult — requiring high-quality recording, assessment of QRS duration and morphology, dynamics, and clinical context
- Artifact or muscle tremor: irregular, changes from beat to beat, not strictly tied to the end of the QRS
- Terminal QRS notching in nonspecific intraventricular conduction delay: usually diffuse, not limited to V1–V3
- Osborn wave: located at the onset of the ST segment in hypothermia, broad and dome-shaped, found in many leads rather than just the right precordial ones
Clinical significance and management
The epsilon wave is one of the surface ECG markers of arrhythmogenic cardiomyopathy. It was a major depolarization criterion in the revised 2010 Task Force criteria for the diagnosis of right ventricular ACM, but it is not sufficient proof of the diagnosis on its own: modern algorithms evaluate it only in the context of the full set of criteria (structural ventricular changes on echocardiography or MRI, biopsy data, nature of ventricular arrhythmias, family history) and after excluding mimics.
Its detection requires referring the patient for a comprehensive evaluation: echocardiography, cardiac MRI to assess ventricular structure and function, Holter monitoring, and, if necessary, a signal-averaged ECG to look for late potentials as an additional sign of the substrate. If there is doubt about the reliability of the finding on the initial tracing, a high-quality repeat standard ECG is needed.
Clinical risk is related not to the wave itself, but to the underlying condition: arrhythmogenic cardiomyopathy is associated with a risk of ventricular tachycardia, ventricular fibrillation, and sudden cardiac death, especially in young individuals and athletes. In confirmed cases, the physician assesses the risk of SCD based on clinical, instrumental, and familial data and determines the need for physical activity restrictions, antiarrhythmic therapy, and implantable cardioverter-defibrillator placement according to current guidelines.
Common interpretation errors
- Confusing the epsilon wave with recording artifacts or muscle tremor without re-checking at different calibrations
- Searching for the epsilon wave only in standard 12 leads without using additional amplification or SAECG when there is a justified suspicion
- Making a diagnosis of ACM based solely on the presence of an epsilon wave without structural ventricular assessment and other criteria
- Failing to account for the fact that the absence of an epsilon wave on a surface ECG does not rule out ACM — the wave is detected in only a fraction of patients
- Confusing it with QRS notching in right bundle branch block
1. In which leads is the epsilon wave best detected?
The epsilon wave reflects delayed right ventricular activation and is best seen in the right precordial leads V1–V3.
2. Which condition is most characteristically associated with the epsilon wave?
The epsilon wave is a classic, though not always present, major criterion of the 2010 Task Force criteria for arrhythmogenic cardiomyopathy.
3. Where in relation to the QRS is the epsilon wave located?
It is a delayed, fragmented potential arising from slowed conduction in an altered area of the myocardium, which is why it is recorded after the end of the normal QRS.
Frequently asked questions
What is an epsilon wave on an ECG?
It is a small deflection or notch immediately following the end of the QRS and preceding the ST segment, best seen in V1–V3. It presumably reflects late fragmented activation of a region of ventricular myocardium altered in arrhythmogenic cardiomyopathy.
Is an epsilon wave dangerous?
The wave itself is not dangerous, but it is a marker of arrhythmogenic cardiomyopathy, which carries an increased risk of ventricular tachyarrhythmias and sudden cardiac death. Its detection warrants a comprehensive cardiological evaluation.
How to distinguish an epsilon wave from a right bundle branch block?
The block produces a wide QRS with typical rSR' morphology in V1 and a wide S in I and V6. An epsilon wave is an additional, separate small potential following the end of the main QRS, but complete RBBB and nonspecific terminal activation delay can create similar notching, thus requiring a high-quality recording, assessment of QRS morphology, and clinical context.
Why is the epsilon wave not always visible on a standard ECG?
The wave amplitude is small (on the order of tens of microvolts), and with standard calibration and recording speed, it may merge with the end of the QRS complex or the ST segment. Increased gain and high-quality repeat recording improve detectability; SAECG additionally detects late potentials from the same substrate, but does not confirm the epsilon wave itself.
Is the epsilon wave included in the diagnostic criteria for ARVC?
Yes, this is a major depolarization criterion in the revised 2010 Task Force criteria for arrhythmogenic right ventricular cardiomyopathy (ARVC). However, the diagnosis is established based on a combination of structural, histological, arrhythmic, and familial data rather than a single epsilon wave.
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Related terms
More in the «Channelopathies and Cardiomyopathies» section
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, current edition
- Orlov V.N. Guide to Electrocardiography
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the ECG, 2009
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.